GB2497845A

GB2497845A - Fuel cell system with desulfurisation device and sulfur sensor

Info

Publication number: GB2497845A
Application number: GB1221549.7A
Authority: GB
Inventors: Frank Baumann; Wolfgang Friede
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2011-11-30
Filing date: 2012-11-29
Publication date: 2013-06-26
Anticipated expiration: 2032-11-29
Also published as: GB2497845B; DE102012221461A1

Abstract

The present invention relates to a fuel cell system 1 having a fuel cell stack. In order to achieve a particularly effective replacement of a desulfurisation device 10 and to protect the fuel cell system 1 from damage caused by sulfurous substances, the fuel cell system 1 comprises at least one fuel cell 2, an anode gas conduit 9 for supplying anode gas to the fuel cell 2, a cathode gas conduit 15 for supplying cathode gas to the fuel cell 2, a desulfurisation device 10 for removing sulfurous substances from the anode gas, and a sulfur sensor (36, figures 2, 3, 5, 7 & 8) for detecting the sulfur content of the supplied anode gas being provided. The present invention further relates to a method for operating a fuel cell system 1 and to the use of a fuel cell system 1 of this kind. The sulfur sensor may be a chemical and/or electrochemical sensor, and most preferably comprises a catalyst such as Ni, Pd, Pt or mixtures thereof which is poisoned by the sulfurous substance. The sulfur sensor may be provided in the anode gas conduit 9, in an anode waste gas conduit 25, and/or in a separate sensor conduit (37, figures 2, 3, 5, 7 & 8) branching off from the anode gas conduit 9 and/or the anode waste gas conduit 25. The fuel cell system 1 may include a reformer 6 for preparing the anode gas.

Description

Description Title

Fuel cell system and method for operating a fuel cell system The present invention relates to a fuel cell system and to a method for operating a fuel cell system.

Prior art

Combined heat and power generation is playing an.

increasingly important role in the energy ruaket because of its potential for reducing the 002 emission for the provision of power and heat. In this respect, fuel cell plants based on ceramic cells (SOFOs) which are operated at high temperature (for example 650 -1000°C) are particularly interesting because of their high electrical efficiency (for instance up to 60%) These plants are often operated on natural gas from the natural gas network.

Important challenges are to achLeve a highest possible electrical efficiency as well as a long service life of the * cells.

The document [iS 6,6&2,836 82 describes a method for operating a fuel cell system. Inthis method, a control system is used to lead the educts in a controlled manner into the fuel cell, in order thus to be able to influence the combustion process. For this purpose, the waste gas of H the fuel cell is examihed by means of a lambda probe, or the characteristic parameters regarding the hydrogen concentration are measured by means of a sensor. - * .-* .,.

The document DE 10 2010 001 011 Al describes a method for operating a combined heat and power plant. In a method of this kind, a first part of a fuel is converted in a fuel cell, thereby generating electrical power, and a second part of the fuel is burnt in an afterburner, thereby generating heat.

* Disclosure of the invention

The subject-matter of the present invention is a fuel cell system having a fuel cell stack, comprising H * -at least one fuel cell; -an anode gas conduit for supplying anode gas to the fuel cell; -a cathode gas conduit for supplying cathode gas to the fuel cell; and -a desulfurisation device for removing sulfurous substances from the anode gas, -a sulfur sensor for detecting thesulfur content H of the supplied anode gas being provided.

A fuel cell system of this kind may thus comprise as central unit a fuel cell stack having at least one fuel cell. In particular, the fuel cell stack may have a plurality of fuel cells which may be of planar.and/or tubular configuration. In this case, the term fuel cell stack is not to be understood in the limiting sense of the * fuel cells being arranged in a stacked manner.

The fuel cells are in this case not limited in their design and may be freely selectable, for example, as regards type and material of the anode and cathode, as regards type and material of the eledtrolyte and as regards the anode and 0 cathàde gas. For example, the fuel cells ma be configured as solid oxide fuel cells. In this case, an electrolyte may be arranged between the anode and *the cathode. in a manner known per se.

Furthermore, the fuel cell system may expediently comprise a connection or an interface for connecting an anode gas source and a connection or an interface for connecting a cathode gas.source. The type of the respective gas source is not limiting. For examp1e, the anode gas source may be a source of natural gas, liquefied gas, hydrogen or.a * hydogen-containing gas, whereas the cathode gas source - may, for example, be a source for oxygen or an oxygen-containing gas, such as, for instance,, air. The anode gas source and the cathode gas source arc in this case connected respectively to the anode and to the cathode in such a manner,, for instance via a suitable anode gas conduit and cathode gas conduit, that anode gas and cathode gas, is leadable to the anode and to the cathode.

Consequently, anode gas in the meaning of the present' invention may in particular be the gas led to the anode, whereas cathode gas may in particular be the gas led to the cathode.

In particular, the fuel cell system may be a reformer for preparing anode gas. This configuration is in particular advantageous for the use of a fuel cell which operates with natural gas as the anode gas. Here, the hydrocarbon compounds present in the natural gas at the anode, for example, of a high-temperature fuel cell, may possibly be unreactive or of only limited reactivity. However, they may be qonverted for example into hydrogen and carbon monoxide by a reforming reaction. Such a reforming may in this case * proceed alongside a reaction on the catalytic anode surface * * * *** * -in particular in the reformer or prereformer arranged before the anode inlet. . Since natural gas, for example, often comprises sulfurous substances or has sulfur cothpounds added to it as odorants in the natural gas network, the fuel cell system may comprise a desulfurisation device foi-removing sulfur or sulfurous substances from the anodegas. Sulfurous substances here may, in the meaning of the present invention, . in particular be pure sulfur or substances which at least partly cothprise sulfur and/or sulfur compounds.

By means of a desulfurisation device of this kind, it is therefore possible to remove sulfurous substances from the anode gas flow and thus prevent sulfurous substances of this kind from passing into the reformer or into the fuel cell or the fuel cell stack, where they could cause damage to these components.

A desulfurisation device may in this case be based in particular on physical and/or chemical adsorption processes. It thay furthermore be configured as a cartridge or as replaceable component, which is often not designed for the entire service life of the fuel cell system, for example ewing to volume demands on the fuel cell system, but may. be configured as a replaceable element for defined intervals. . * * * * In order, for example, to be able to organise a replacement of devices of this kind particularly efficiently, a sulfur sensor for detecting the sulfur content of the supplied anode gas is provided. By means of this sensor, the sulfur content of the anode gas may be determined and thereby equally the sulfur charging of a desulfurisation device may

S

be determined. The sulfur content in the meaning of the present invention may be understood as in particular the concentration of sulfur or of sulfurous subètances in particular in the anode gas. In this case, in a manner evident to a person skilled in the art, by measuring the sulfur content in the anodewaste gas it is possible to determine indirectly likewise the sulfur content in the anode gab.

By means of a sulfur sensor of this kind, it is thus advantageously possible to determine what concentration of sulfurous subtances isactually present in the anode gas and what amount of sulfurous substances has already been removed from the anode gas by the desulfurisation device. -As a result, it is possible to react. to the fact that the sulfur content of the gas varies at different locations and also fluctuates over time. tt can thus be ascertained in a defined and reliable manner and in advance when a desulfurisation device should be replaced or when a sulfur breakthrough, which is damaging to the fuel cell system, is to be expected.

It is thereby possible, firstly, to prevent the desulfurisation device br the cartridge from having to be overdimensioned and/or from being replaced before a greatest possible charging is reached. Rather, the Leplacement intervals may be designed according to requirements, so that the cartridges employed can be optimally utilised. As a result, costs can be saved.

Furthermore, even in the case of an unexpectedly high concentration, such as, for instance, a surge odorising, of sulfur or of sulfurous substances, damage to the fuel cell system can be prevented. The system is thus protected from S.. damage due to unexpectedly high sulfur concentrations in the anode gas used, such as, for instance, in natural gas used.

In the context of one configuration, the sulfur sensor may be based on a chemical and/or electrochemical reaction. In particular, the sulfur sensor may be based on a reaction of the anode gas with oxygen. In this case, the strength of the reaction may. decrease as a function of the sulfur content. Furthermore, in this configuration, the sulfur sensor may comprise at least one catalyst which can be poisoned by a sulfurous substance. In this case, the sulfur content may be determinable from the decrease of the strength of the reaction, which nay be measurable, for example electrically and/or thermally. In this configuration, a determination of the sulfur content may be based in particular on an influencing or poisoning of the sulfur sensor. In this case, the influencing or poisoning is caused by the presence of sulfurous substances and is in particular a function of the content of sulfurous bompounds, i.e. of their concentration. Thus, by the influencing of the mode of operation of a sulfur sensor, i.e. in particular by the influencing or the decrease of the strength of a chemical and/or electrochemical reaction of the sulfur sensor, it is possible to infer the content of sulfurous substances.in the anode gas.

In the context of a further configuration, the sulfur sensor may be formed as a catalytic and/or electrochemical * sensor, in particular the sulfur sensor being able to.

:. : comprise or be a combustion catalyst, a fuel cell or a * lambda probe. Sulfur sensors of this kind may be able to be formed particularly cost-effectively and may in this case be particularly sensitive and selective in particular with regard to sulfur or sulfurous substances. Moreover, even at high temperatures, sulfur sensors of this kind have particularly long-term stability and work reliably.

-Furthermore, it may b possible to control sulfur sensors of this kind by control devices or peripherals present in a fuel cell system anyway or be able to evaluate the determined data. As a result, sulfur sensors of thiskind may be capable of integration particular]y cost-effectively and with a simple construction also in already existing fuel cell systems.

In this case, sulfur seisors of this kind may furthermore be based on a particularly advantageous measuring method.

In detail, the evaluation may be based, for example *in this configuration, on the fact that the sulfur sensor is poisoned by sulfurous substances and hence no longer works as desired. Consequently, in this configuration Of the * sulfur sensor, in particular a deviation from a standardised and defined mode of operation may serve for * the sulfur determination. In the case of a combustion catalyst, for example, the oxidation of the anode gas may serve for the sulfur determination. In this case, for the oxidation of the anode gas in particular the supply of cathode gas as oxygen source for a donthustiOn of the anode gas or anode waste gas may be advahtageous, since in a fuel cell system there is in most cases already provision for a precisely regulated control of the cathode gas supply.

Regarding an electrochemical sensor, which may in particular be a fueF cell, the latter may be poisoned * likewie by sulfurous substances, and this may be detectable for example by a reduced generation of electrical energy: Furthermore, a lambda probe may also operate with reduced performance due to a sulfur poisoning.

Thu, the sulfur sensor can detect the concentration of S sulfurous substances in particular via a sulfur poisoning and hence a restricted reaction with the anode gas.

In the ccntext of a further configuration, the catalyst of the sulfur:sensor may comprise nickel,. palladium, platinum or mixtures thereof, or consist of the aforementioned materials. In particular as a catalytic sensor, sulfurous substances or sulfur can be detected and determined particularly sensitively and selectively. For example, the sulfur sensor in this configuration may be supplied with an oxygen-containinygas, such as, for example, the cathode gas, for instance air, besides the anode gas, in order to * be able to catalytically oxidise the anode gas and to be able to use parameters associated with the catalytic oxidation for determining the concentration of sulfur or of sulfurous substances. In this case, materials of this kind may furthermore be poisoned in a suitable manner by sulfurous substances for a good evaluation. Furthermore, materials of this kind are in most cases present anyway in a fuel cell system, so that a fuel cell system in this configuration may be able to be formed particularly cost-effectively.

* In the context of a further configuration, the sulfur sensor maybe arranged * * -in the anode gas conduit and/or -in an anode waste gas conduit for discharging * anode waste gas from the fuel cell and/or -* in a sensor conduit branching off from the anode fl.*.

* * gas conduit and/or from the anode waste gas conduit.

:. * In this configuration, the sulfur sensor may be arranged * particularly favourably in order to be able to detect a concentration of sulfurous substances in the anode gas or anode waste gas reliably and accurately. In the arrangement of the sulfur sensor in an anode gas conduit or anode waste gas conduit, the sulfur sensor comes into contact, with a particularly simple construction, with the anode gas or with the anode waste gas, in order to determine the content of. sulfurous substances. In an arrangement in a sensor conduit, the sulfur sensor may be independently temperature-controlled. Moreover, oxygen-containing gas may be conducted to the sulfur sensor in a particularly simple manner under defined, conditions, in order, for example, to provide oxygen for an oxidation of the anode gas. This may be realised, for example, by a suitable cathode gas conduit.

or cathode waste gas conduit which can open into the sensor conduit.

Regarding the sensor conduit, in this case furthermore a suitable volume of anode gas may be supplied to the sulfur sensor, without howàver substantially influencing the flow of anode gas. As a' result, it is possible, for example if the anode gas flow is divisible in,a suitable manner by valves into a partial flow flowing through the sensor conduit and into a partial flow flowing to the anode, on' the one hand for the fuel cell always to operate as desired and with a suitable anode gas flow, and on the other hand, however, for the sulfur sensor always to be supplied with the same and constant volume of anode gas, so that also the measuring conditions may always be constant. In this * configuration, in particular the anode gas flow led through the sensor conduit and the anode gas flow led to the anode may be adjustable independently of one another. A branching-off from the anode gas' conduit may in, this case equally comprise,a branching-off from the desulfurisation device arranged in the anode gas conduit.

In the context of a further configuation, the anode gas conduit and/or the anode waste gas conduit and/or the sensor conduit may have an inner coating, the inner coating comprising the catalyst of the sulfur sensor. This is a particularly simple and effective configuration in order to be able to measure the sulfur content in the anode gas or in the anode waste gas-In detail, the catalyst may be deposited by a conventional coating r4hod, for example, on the inner surface of a gas cbnduit, such as, for example, a pipe, which may save costs and be simple in terms of production. 4oreover, the catalyst maybe brought into contact with the anode gas in a particularly simple manner by a simple flow through the gas conduit, the catalyst furthermore having a particularly large surface and thereby being able to be particularly active.

In the context of a further configuration, the sulfur sensor may be arranged in gas-conducting connection, in particular in direct gas-conducting connection, with the deSulfurisation device. In this configuration, the concentration to be detected may be determinable particularly accurately. This is because the, in particular, direct and immediate gas-conducting connection between desulfurisation device and sulfur sensor enables the sulfur sensor to immediately measure the gas flow which flows through the desulfurisation device and thuâ always deliver correct and reliable data immediately associated * S S * S * with the operation of the desulfurisation device. A gas-*5.t..

* conducting connection may in this case be realised, for *:*. example, by a gas conduit, such as, for example, a pipe, or in another manner known in principle to a person skilled in the art. S. -* * * *5*

In the context of a further configuration, the * desulfurisation device may have a specific flow stretch for the anode gas and the sensor conduit may branch off from the desulfurisation device at a place lying in a range from »= 50 to «= 90% of the flow stretch for the anode gas, or the sulfur sensor may he arraned at a place lying in a range from »= 50 to «= 90% of the flow stretch for the anode gas.

In this configuration, a particularly accurate detection of the content of sulfurous substances is possible, since here essentially only one sulfur breakthrough needs to be detected. In detail, no sulfur is detected as long as the desulfurisation device upstream of the branching-off or of the sulfur sensor operates as desired. If, however, the desulfurisation device, or the region arranged in a starting region, operates only to a limited degree, for instance due to a high degree of charging, and thereby allows sulfurous substances to pass, this can be determined * by the sulfur sensor. In this case, it may in particular be advantageous for the sulfur sensor to be arranged at a place, or for the sensor conduit to branch off from a place, downstream from which in the flow direction of the anode gas there is still a residual capacity of uncharged and thus correctly operatingdesulfurisation device available, so that it is not immediately necessary to replace the desulfurisation device. In this case, the further possible operational life may be formed in particular as a function of the precise arrangement of the branching-off of the sensor conduit or of the sulfur * sensor. For example, a suitable place for the sulfur sensor "S...

* or for the branching-off of the sensor conduit may be in the last third of the desulfurisation device in the flow direction of the anode gas. For example, such a point may :. be arranged in the flow direction of the anode gas at a * place ranging from »= 75% to «=90% of the flow stretch of S the desulfurisation device, with thus still a range from > 10% to < 25% of the flow stretch downstream of the sulfur sensor or the branching-off being provided. These values are, however, purely by way of example and may be dependent on the sulfur loading of the anode gas to be expected and the desired lead. time until a failure of the desulfurisation device. The above values may be valid, for example, for a replacement interval of the desulfurisation device of two years and a lead time of 2 to 3 months.. The flow stretch may in this case mean in particular the.

distance traversed by the anode gas.

In the context of a further configuration, a temperature sensor for determining the -temperature of the sulfur senor and/or of the * sensor waste gas may be provided, and the sulfur content may be determinable from a decrease of the temperature pf the sulfur sensor and/or of * the sensor waste gas, and/or -a voltage and/or current and/or resistance measuring device for determining current, resistance and/or voltage of the sulfur sensor may be provided, the sulfur content being determinable from a change of the voltage and/or the current and/or the resistance of the sulfur sensor.

In this cbnfiuration, a detection of the content of * S U sulfurous substances may be evaluated in a particularly * advantageous manner. In detail, a temperature senor as -**j well as a voltage and/or current and/or resistance * measuring device can be implemented cost-effectively in a fuel cell system. Furthermore, by a measuring method of * " * this kind, even small changes of the temperature or of current, resistance or voltage are detectable, so that a sulfur sensor in this configuration may be particularly sensitive.

A temperature sensor in this case may be advantageous in particular in the use of a combustion catalyst in a sulfur sensor, since here, through a combustion of the anode gas and/or anode waste gas, a temperature increase is achieved - which may be detectable in a simple manner. In this case, -through a decreasing temperature, a diminishing reactivity of the catalyst can be determined. If the reactivity of the catalyst decreases, this allows an inference of the poisohing of the catalyst and hen6e correspondingly of the sulfurous substances in the anode gas which cause the poisoning. A determination of the temperature of the sulfur sensor may in this case mean, for example, a determination of the temperature of a sensor housing orof the catalytic surface itself. A temperature sensor may in this case furthermore be arrangeable with little outlay and require few peripherals for a suitable evaluation.

Regarding a voltage and/or current and/or resistance measuring device, this may be advantageous in particular for an electtochemical sulfur sensor,, such as, for example, a fuel cell, since here a voltage or a current may be generated for instance by the evaluation of the anode gas or of the anode waste gas,, the fuel cell having an internal resistance, which parameters may be advantageously determinable, since both the internal resistance of the fuel cell and the generated voltage or-the generated current is dependent on a poisoning by sulfurous substances. -- * - d --In the context of a further configuration, the sulfur sensor may be arranged in gas-conducting connection with the cathode gas conduit and/or a cathode waste gas conduit for discharging cathode waste gas from the fuel cell, and/cr an air supply. In this configuration, it is thus possible, for the provision of a èombustion catalyst in a * particularly simple and cost-effective manner, to supply the sulfur sensor with oxygen in order to be able to oxidise or burn anode gas or anode waste gas. Through the use of a cathode gas conduit or cathode waste gas conduit, it is thus possible to use a flow of oxygen-containitig gas * which is regulated by the fuel cell system anyway, thus enabling a particularly simple regulating response. With regard to an air supply, in particular one dedicated and hence separated from the cathode gas conduit or cathode waste gas conduit, this air supply may be regulable particularly freely and independently of a cathode gas flow or cathode waste gas flow.

In the context of a further configuration, the sulfur sensor may be beatable by a thermal coupling to a beatable part of the fuel cell system by waste heat arising during the operation of the fuel cell system. In this configuration, on the one hand, a particularly simple and energy-saving heating of the sulfu sensor may be possible.

Moreover, the sulfur sensor, for example in the case of the use as a catalytic sulfur sensor, may be particularly * active and furthermore sensitive. In this configuration, *4 * * the sulfur sensor may be ih particular thermally coupled to * . a part of a so-called hotbox, i.e. the heated or heatable *rs part of the fuel cell system. This may enable heating of the sulfur sensor by a part of the fuel cell system which may be temperature-regulated in a suitable manner already * t* * by the operation of the *fuel cell system. It is thus S possible to resort in particular to a temperature source which is regulated as accurately as possible anyway, so that a heating of the sulfur sensor may be possible in a particularly simple and cost-effective manner.

In the context of a further configuration, the sulfur sensor may be integrated in a heat exchanger, in a reformer, and/or in an afterburner. These may be -particularly suitable positions in order tq heat the sulfur sehsor by components of the fuel cell system which are mostly thermally-regulated as accurately as possible anyway, since here mostly a very accurate temperature control takes place.

In the context of a further configuration, a sulfur charging of the desulfurisation device may be determinable as a function of the sulfur content deterthined b' the sulfur sensor, in particular in which case a warning, in particular to renew the desulfurisation device, may be issuable when a predetermined limit value of the sulfur charging is exceeded. In this configuration, by an evaluation of the data determined b' the sf sensor, it is thus possible to infer the charging of the desulfurisation device. In the case where the charging of the desulfurisation device exceeds a predetermined limit value, the desulfurisation device may be renewed after a warning has been issued. A renewal of the desulfurisation device may in this case mean, in anon-limiting manner, a regeneration, in particular a removal of the absorbed S..... -* S sulfurous substances, or else a replacement of -the *. . *, desulfurisation device or of the active part of the desuifurisation device, such as in particular a desulfurisation cartridge.

-In the context of one configuration, the fuel cell system may have a conroi unit for evaluating the data of the sulfur content which are determined by the sulfur sensor.

In this configuration, it may particularly advantageously be ensured that the concentration, determined by the sulfur sensor, of sulfurous substances present in the anbde gas may be evaluated with regard to the desulfurisation.

performance of the desulfurisation device and where necessary a warning or a sign may be issued to renew the desulfurisation device or shut down the fuel cell system, in the case of an aithost full charging or a sulfur breakthrough.

with regard'to further advantages and technical features of the fuel cell system according to the invention, reference is hereby made explicitly to the explanations in connection with the method according, to the 4nvention, the figures,

and.the description of the figures.

The subject-matter of the present invention is furthermore a method for opeating a fuel cell system, -in particular a fuel cell system according to the invention, comprising the method steps:.

a) leading an anode gas to the anode of a fuel cell; b) leading a cathode gas to the cathode of a fuel cell; c) removing sulfurous substances from the anode gas by a desulfurisation device, ahd d) determining the concentration of sulfurous substances * in the. anode gas by a sulfur sensor.

*0**. . * * . . * By the above-described method, it is possible to determine what concentratioi of, sulfur or of sulfurous substance's is actually present in the anode gas or has occurred overall : -over a defined period of time. As a result, it is possible to react to the fact that the sulfur content of the gas varies at different locations and also fluctuates over time. It can thus be ascertained in a defined and reliable manner and in advance when a desulfurisation device should be replaced or when a sulfur breakthrough, which is damaging to the fuel cell system, is to be expected.

In the context of one configuration, the sulfur content may be determined by a sulfur poisoning of the sulfur sensori This is a paticuiarly simple, reliable and accurate possible way of determining the concentration of sulfurous substances.

With regard to further advantages and technical features of * the method according to the invention, reference is hereby made explicitly to the explanations in connection with the fuel cell system according to the invention, the figures,

and the description of the figures.

The subject-matter of the present invention is furthermore the use of a fuel cell system, which may be configured as described above, in combined heat and power plants or engine-based cogenerators. Combined heat and power plants * may in this case in particular be plants which provide useful heat, for example for heating purposes or else for production processes, in particular while simultaneously generating electrical energy. A plant of this kind may thus decouple useful heat during the power geheration by means * * * of fuels. In this case; in particular a use in fuel-cell * * heating apparatuses, combined heat and power generation or * engine-based cogenerators of different power clas, such * as, for instance, »= 0:5 to over 1000 kW, may be possible. * * * ***

Further advantages and advantageous configurations of the subject-matters according to the invention are illustrated by the drawings and explained in the following description.

It should be noted that the drawings have merely a descriptive character and are not intended to limit the invention in any form, In the drawings Fig. 1 shows a schematic illustration of one configuration of a fuel cell system; Fig. 2 shows a schematic illustration of one configuration of an arrangement comprising desulfurisation deviceand sulfur sensor; Fig. 3 shows a schematic illustration of the configuration.from Figure 2; Fig. 4 shows a schematic illustration of the measured values of a sulfur sensor over time; * Fig. 5 shows a schematic illustration of a further configuration of.an arrangement of a sulfur sensor; Fig. 6 shows a schematic illustration of the measured values of the sulfur sensor from Fig. 5 over time; Fig. 7 shows a schematic illustration of a further configuration of an arrangement of a sulfur sensor; and Fiq. 8 shows a schemaLicillustration of a further configuration of an arrangement of a sulfur sensor. * . * . * *

Figurel shows a schematic illustration of one embodiment * of a fuel cell system 1. A fuel cell system 1 of this kind may he used, for example, in combined heat and power planté, or in engine-based coge-nerators, or else in motor * -* vehicles. * According to Figure 1, the fuel cell system 1 comprises a fuel cell stack with at least one fuel cell 2, such as, for instance, a solid oxide fuel cell, with an anode 3 and a cathode 4. In this case, an electolyte 5 is arranged between the anode 3 and the cathode 4, anode gas and cathode gas being converted in the fuel cell 2 électrochemically into poker and heat. Expediently, the fuel cell system 1 further comprises an electrical connection (not illustrated) for tapping electrical energy from the fuel cell 2 or from the fuel cell stack formed from a plurality of fuel cells 2-The fuel cell system 1 may further comprise an anode circuit, for instance with a suitable gas conveying unit, as well as heat exchangers for recirculating anode waste gas.

Furthermore, the fuel cell system 1 may have a reformer 6 for carrying out a reforming reaction and for processing anode gas, depending on the desired fuel gas.used.

The fuel cell system 1 may further have a connection for connecting an anode gas source 7 or for withdrawing anode gas from the anode gas source 7, which source is fluidically connected to an anode gas inlet 8 of the fuel cell 2 by an anode gas conduit 9. Expediently, in this case the anode gas may pass through the refbrmer 6. In the anode gas conduit 9 there may be provided, for instance, a desulfurisation device 10, as will be explained later in * . detail with reference to Figures 2 to 8, as well as a suitable gas conveying unit 11, such as, for instance, a compressor, and a valve 12. The desulfurisation device 13 may, for example, be replaceable and, for instance, be configured as a cartridge. In addition, a waterinput device, such as, for instance, an evaporator 47, may be provided.

Furthermore, the fuel cell system 1 may have a connection for connecting a catiode gas source 13 or for withdrawing cathode as from the cathode gas source 13. The cathode gas may be conveyed, for instance, by a suitable gas conveying unit 14, such as, fdr instance, a compressor, into or in a cathode gas conduit 15. The cathode gas conduit 15 may further be connected to.a cathode gas inlet 16 of the fuel cell 2. In the cathode gas bonduit 15, in this case, one or a plurality of heat exchangers 48 may be arranged, which preheat the cathode gas, forexample, by an interaction with the fue1ce11 waste gas.

Furthermore, a further cathode gas path 17; for instance with a further gas conveying unit 18, may be provided, which path branches off with a valve 19 from the cathode gas conduit 15. The cathode gas path 17 nay in this case, for example, be used for starting the fuel cell system 1 andlor concluctThg cathode gas, for instance via a water input device or an evaporator 47, into the reformer 6 for a reforming reaction.

A cathode waste gas conduit 21 connected to a cathode waste gas outlet 20 may be connected to an afterburner 23, for example via heat exchangers fd preheating the cathode gas, as indicated by the arrow 22, so that cathode waste gas can * * be led to the afterburner 23. By means of the afterburner ** * 23 it is possible to oxidise, for example fuels present in the anode waste gas, such as, for example, carbon monoxide (00) to form carbon dioxide (002) orhydrogen (B2) to form water, using the cathode waste gas flowing out of the cathode 4 as oxidising-agent. For this purpose, anode waste gas can be led front an anode waste gas outlet 24 through an anode aste gas conduit 25, for example by providing * corresponding valves, to the afterburner 23.

The afterburner 23 may be connected, for example, to the reformer 6. li-i addition, there may -be provided downstream of the afterburner 23 a waste gas line 26 which, in particular thermally connected to the heat exchanger 48 or the evaporator 47, may be connected to an outlet 27, it being possible for the waste gas line 26 to be part of the anode waste gas conduit 25 cr and/or of the cathode waste gas conduit 21. Upstream of the outlet 27 of the fuel cell system 1 there may be provided a further heat exchanger 28 which may be conxected to a device for utilisation of heat.

In addition, there may be provided a condensation device (not illustrated) which can condense water and supply it via a conveying device 29 to a water input device 30. Water may be supplied to the latter furthermore by a water source 31, for instance via a valve -32. The water input device 30 may then supply water to the anode gas-conduit 9, for -instance by a conveying device 33 and by a water conduit 34. -- Furthermore, 35 designates one configuration of the -so-called hotbox, i.e. the hot or beatable part of the fuel cell system 1. -* . * * * * In the following, in particular the desulfurisation device and components associated therewith are explained in detail. * S * S..

One configuration of the fuel cell system 1 is shown in Figure 2. In Figure 2, firstly the desulfurisation device 10, arranged in the anode gas conduit 9, for removing sulfurous substances from the anode gas is shown. It can further be seen from Figure 2 that a sensor for detecting the sulfur content of the supplied anode gas, referred to hereinbelow as sulfur sensor 36, is provided. In this case, the sulfur sensor 36 may be configured as a catalytic sensor and/or as an electrochemical sensor. In particular, the sulfur sensor 36 may comprise a combustion catalyst, a fuel cell or a lambda probe, as explained later in detail.

Thus, the sulfur sensor 36 may be based on a chemical and/or electrochernical reaction, in particular of the anode gas with oxygen, the strength of the reaction decreasing as a function of the sulfur content, in particular the sulfur sensor 36 comprising at least one catalyst which can be poisoned by a sulfurous substance, in particular the sulfur * content beingdeterrninable from the deOrease of the strength of the reaction, in particular which is, for example electrically and/or thermally, measurable. Thus, a deterthination of the sulfur content may be determinable in particular by a sulfur poisoning of the sulfur sensor 36.

In the configuration as a catalytic sulfur sensor 36 or as a combustion catalyst, for example, it may serve in particu]ar to cxidise anode gas, the catalyst losing activity due to sulfur charging of the anode gas. By detection of specific parameters of this reactiOn, the * poisoning can be followed and hence the sulfur content in S. * * .t the anode gas and furthermore the charging of the desulfurisation device 10 inferred. For example, the sulfur sensor 36 may comprise nickel, palladium, platinum or mixtures thereof. Furthermore, the catalyst of the sulfur sensor 36 may be arrangedin this configuration in a combustion space and/or delimit the latter, in which space the fuel gas or anode gas to be supplied is converted with oxygen-containing gas, such as, for instance, the cathode gas or cathode waste gas, for example air.

In this case, as shown in Figure 3, there may further be provided a temperature senior 41 for determinin the temperature of the sulfur sensor 3 and/or of the sensor waste gas, the ulfur.content being determinable froin a decrease of the temperature of the sulfur sensor 36 and/or of the sensor waste gas, which is a measure of the oxidation of the anode gas. Additionally or alternatively, there may further be provided, depending on the configuration of the sulfur sensor 36, a voltage and/or current and/or resistance nieasuring device for determining &srrent, resistance or voltage of the sulfur sensor 36; the sulfur content being determinable from a change of the voltage and/or of the., current and/or of the resistance of the sulfur sensor 36, as explained later.

Furthermore, the sulfur sensor 36 may be thermally coupled * to a partial region of the fuel cell system 1, which region is thermally regulated anyway, for instance by thermal couplingtb the hotbox. mother words, the sulfur sensor 36 may be heatable by a thermal coupling to a heatable path of the fuel cell system 1 by waste heat arising during the operation of the fuel cell system 1. Suitab]e positions for * the sulfur sensor 36 in this case comprise a heat exchanger * S 47, a reformer 6, and/or in an afterburner 23, in which the *S S ** *; sulfur sensor.36 may be integrated.

The sulfur sensor 36 may furthermore be arranged in the * anode gas conduit 9 and/or in the anode waste gas conduit to discharge anode waste gas from the fuel cell 2 and/or in a sensor conduit 37 branching off from the anode gas conduit 9 and/or the anode waste gas conduit 25. In this * case, the sulfur sensor 36 may be arranged in gas- * conducting connection, in particular in direct gas-conducting connection, with the desulfurisation device 10.

According to Figure 2, the sulfur sensor 36 is arranged in the sensor conduit 3?, which branches off from the anode gas conduit 9 and in particular is routed parallel to the anode gas conduit 9. The anode gas led through the sensor conduit 37 may in this case be conducted, for example, into theafterburner 23 or in an cutlet of the fuel cell systen' 1. For example, the anode gas supply conduit 9 and/or the anode waste gas conduit 25 and/or the sensor conduit 37 according to Figure 2 may have an inner coating, the inner coating comprising the catalyst of the sulfur sensor 36.

In this case, the desulfurisation device 10 may have a specific flow stretch for the anode gas and the sensor conduit 3? may branch off from the desulfurisation device *at a place lying in a range from »= 50. to «= 90% of the flow stretch for the anccde gas, or the sulfur ènsor 36 may be arranged at a place lying in a range from »= 50 to «= 90%.

of the flow stretch for the anode gas. For example, the sensor conduit 37 may branch off approximately after of the run length of the desulfurisation device 10, or the sulfur sensor 36 itself may be arranged approximately after * of the run length of the desulfurisation device 10. The * * branching-off or the sulfur sehsor 36 itself may also be arranged between two in particular identical desulfurisacion devices 10, so that in the event of a replacement the desulfurisation device 10 before the sulfur * " sensor 36, or upstream of the sulfur sensor 36, can be rmoved. The desulfurisation device 10 after the sulfur sensor 36 or downstream of the sulfur sensor 36 may, for example, be retained, or positioned upstream of the sulfur sensor 36 and replaced by a new desulfurisation device 10.

Preferably, the desulfurisation devicelO, before and after the branching-off or the sulfur sensor 36, may be identically configured. Thus, if for example several different sorbents are provided for the sulfurous substances in the desulfurisation device 10, these may preferably all be provided before and after the branching-off to the sulfur sensor 36 or the sulfur sensor 36 itself.

The sulfur sensor 36 or the sensor conduit 37 may be arranged for instance as a pipe, for example on the inside of a heat transfer device, such as, for instance, the heat exchanger 48 through which air-or waste gas flows, or in a line through which air or waste gas flows, the anode gas flowing through the sensor conduit 37 or the sulfur sensor 36. For example; the sulfur sensor 36 may be arranged in gas-conducting connection with the cathode gas conduit andlor the cathode waste gas conduit 21 for discharging cathode waste gas from the fuel cell 2, and/or an air -supply.

Preferably, it is possible to select for the sulfur sensor 36 a position which is eithe kept at a constant temperature by the system regulation, such as, for * instance, at an identical operating point of the system, or * . the temperature of which is already measured system-dependently. If the sulfur sensor 36 comprises a catalyst, thus, for example, the sensor conduit 37 is coated internally with catalyst, a combustion and hence a -temperature increase may be determinable with simultaneous supply of anode gas and the presence of an oxygen-containing gas flow or air flow, for instance, in the sensor conduit 37. For this purpose, for example cathode air or waste gas an flow through the sensor conduit 37.

Preferably, the same catalyst which can also be used in the reformer 6 or in the fuel cell 2, namely in particular nickel, or else palladium, platinum or mixtures thereof.

Specific installation possibilities for the sensor conduit 37 or for the sulfur sePsor 36 may comprise, for example: the outer wall of the reformer 6, the inner wall of the combustion chamber of the afterburner 23, the inside of the well of the hotbox 35 surrounding the fuel cell 2, or the inside of a heat exchanger 28, 48, for instance, for air preheating or for cathode gas preheating.

The sulfur sensor 36 may operate particularly advantageous, for instance, in a steady state of the system, i.e. when all temperatures are constant. In the configuration of the egions before and after the branching-off or the sulfur sensor 36 itself according to Figure 2, attention may be paid, in particular regarding the positioning, to ensuring that there is sufficient time between th& detection and a breakthrough, in order thus to carry odt a stopping and/or a starting process. This does not constitute a restriction, owing to the service life ot the desulfurisation device 10 of in most cases at least a few months. *o * S * *

In Figure 3, a further illustration of the configuration * * from Figure 2 is shown. Illustrated is the sulfur sensor 36, through. which or along which flows a flow of oxygen-containing gas tThich is marked by the arrow 38 and serves for an oxidation of the anode gas. In this case, this flow may be, for instance, a cathode gas flow, cathode waste gas * 27 flow or burner waste gas flow of the afterburner 23, or branch off from the cathode gas flow, cathode waste gas flow or burner waste gas flow, which is indicated bythe arrow 39. In this case, furthermore, the anode gas flow * which potentially comprises sulfurous substances flows through or along the sulfur sensor 36, for instance through the sensor conduit 37: The sulfur sensor 36 may in this case have a temperature sensor or temperature probe 41, by which the temperature of the sensor waste as or of the sulfur sensor 36 itself, such as, for instance, the temperature prevailing in a combustion chamber of the * sulfur sensor 36, is determinable. The temperature sensor * 41 thus measures the temperature increase whibh arises due to the catalytic oxidation of the anode gas, in particular when a catalytic sulfur sensor 36 is ued. For this purpose, for example a qas-condudting connection from the sulfur sensor 36 to the anode gas or an oxygen-containing gas may be provided. or else both gases may flow through a common pipe.

A temperature measurement enables the ageing state of the * desulfurisation device 10 to be inferred. This is illustrated in Figure 4. Figure 4 shows a graph in which the determined temperature (Ti is plotted qualitatively * against time (t) -It can be seen that up to an instant a) at which there exists a full or almost full charging of that part of the desulfurisation devide 10 which lies upstream of the sulfur sensor 36 or a branching-off to the * sensor conduit 37, the temperature falls slowly due to a * . * slight degradation under normal conditions. From the point ** * * , a) , which may typically lie in a range of 2 years, a * greater degradation takes place due to a sulfur breakthrough, caused by an increasing poisoning of the catalyst.

This temperature measurement may be evaluated in a control unit. In the control, in this case the increase of the temperature over time may be determined, in particular in the case where the system regulation keeps the temperature in the environment of the sulfur sehsor 36 constant.

Instead of the absolute temperature, it is also possible to measure the temperature difference with respect to the environment or to an inflowing gas, such as, for instance, air. If a predetermined limit value or a predetermined -increase is exceeded, a warning may be issued which is visible, for example, by the user or via a communications interface by the maintenance personnel, whereby a replacement of the desulfurisation device 10, such as, for instance, a cartridge, may be ?ccasioned.

Figure 5 shows a further configuration of the fuel cell system 1 according to the invention. In this configuration, a lambda probe 42 may be used as the sulfur sensor 36.

Purely by way of example of the use of a lambda probe 42 as the sulfur sensor 36, this probe may be inserted in the waste gas path after the: cathode 4 or after the afterburner 23. Here, too, the gas to be examined is directed onto the lambda probe 42 or the sulfur sensor 36 or into the seflsor conduit 37, in which case likewise the degradation of the sulfur sensor 36 or of the lambda probe 42 may be measured.

For this purpose, likewise a flow 38 of oxygen-containing gas may be supplied. The measurement may be done on the * basis of the rate of the degradation of the lambda probe 42, as shown in Figure 6. In Figure 6, the signal S of the lambda probe 42 along tine t is shown as óurye A and indicates from a point a) a markedly increasing -degradation.

Alternatively, two lambda probes 42, 43 may be used, one lambda probe 43 in this case being able to serve as reference and the corresponding signals, illustrated by the curve A for the lambda probe 42 and the curve B for the * reference lambda probe 43, being compared, as shown in Figure 6. This may in particular be of interest in systems in which a lambda probe 43 is used anyway for regulation of air mass flow and hence regulation of temperature. Owing to the thermal coupling to a hot or heatabie part of the fuel cell system 1 or the hotbox 35 or owing to an arrangement ma hot region, it is possible to dispense with the heating otherwise customary in the lambda probe 42, 43, whereby costs can be saved.

Figure 7 shows a further configuration of the present fuel cell system 1. According to the configuration shown in Figure 7, the sulfur sensor 36 may be formed as a fuel cell * 44, such as, for instance, as a SOFC fuel cell, for example with a tubular fuel cell 44 equipped with external cathode and internal anode. In this case, the voltage measured by a voltage measuring device 45 mayserve as an indicator of the sulfur content of the anode gas. To avoid coking, here too air may be metered into the, for example internal, anode.

Alternatively, in the configuration according to Figure 8, in the use of a fuel cell 44 as sulfur sensor 36, a current flow may be generated, for example via a resistor 49, and this may give rise to product water on the anode side. The fuel cell 44 may be, for example, a medium-temperature SOFO fuel cell. The current flow generates water on the anode of the fuel cell 44, so that the supply of air onto the anode may be dispensed with arid the inlet side 46 may be closed.

0 The sulfur sensor 36 may also be adapted in its configuration to the current-generating cells in the fuel cell stack and be arranged there, for example, outside the current collector plates (in planar stacks) or outside the current collectors (in tubular stacks) In the use of a fuel cell 44 as sulfur sensor 36, too, the degradation caused by sulfurous substances ray'serve as a measure, of the sulfur content *of the anode gas, for instance measurable by the current flow o the voltage, as described above, or by measuring a resistance of the sulfur sensor 3.6.

The sulfur sensor 36 may in particular be easily accessible and replaceable along with the desulfurisat ion device 10.

Alternatiely, a pluralityof sulfur sensors 36 may' be -installed at the beginning,' which are used one after the other for measureent. If the outlets are combined, a-common temperature measuring point is sufficient. The unused inlets are then closed.

A method for controlling a fuel, cell system 1 of this kind may in this case comprise the following method steps: a) leading an. anode gas to the anode 3 of a fuel cell.2; b) leading a cathode gas to the cathode 4 of a fuel cell 2; c) removing sulfurous substances from the anode gas * by a desulfurisation device 10, and 0'e** * * d) determining the concentration of sulfurous substances' in the anode gas by a sulfur sensor 36.

** . . * S * S..

In particular, the sulfur content in this case may be determined by a sulfur poisoning of the sulfur sensor 36.

A measurement in this case does not need to take place continuously, but may be measured at specific time intervals or at specific operatinq points, in which the ambient tethperature of the sulfur sensor 36 or the air throughflow in the surrounding space is, for example, sufficiently known. In this case, where a sulfur breakthrough is detected or to be expected and hence the desulfurtsation device 10 should be replaced, a warning may be issued.

The supply line of the gas to be measured to the sulfur sensor 36 rny be equipped with a, for example, mechanical or electronic flow limiter, so that even with fluctuating gas pressure the same amount of gas always flows and thus constant measuring conditions prevail.

Furthermore, a plurality -of sulfur sensors 36 may be ---installedwhich are used one after the other in the case where the sulfur sensors 36 are successively poisoned by sulfurous substances. If the corresponding outlets are combined, a common measuring position, such as, for -in-stance, temperature measuring position, may also be sufficient --In apparatuses with a peak load boiler for the heat generation, the sulfur sensor 36 may furthermore be installed in the hot waste gas flow in the vicinity of the burner, even with this peak load boiler. - -The above-described arranqSent of the sulfur sensor 36 -may, in principle, also be used analogously for the detection of other harmful substances, such as, for example, for the detedtion of alkali. Also possible, in principle, is a use in the air path and/or gas path, i.e. in the cathode gas path and/or in the anode, gas path. S. S. * . . * * -* . *5, -* * * * **

-* * * ***

Claims

<claim-text>Claims 1. Fuel cell system having a fuel cell stack, comprising -at least one fuel cell (2); -. an anode gas conduit (9) for supplying anode gas to the fuel cell (2); -a cathode gas conduit (15) for supplying cathode gas to the fuel cell (2); and --a desulfurisation device (10) for removing sulfurous substances from the anode gas, -a sulfur sensor (36) for detecting the sulfur cbnen of the supplied anode gas being provided.</claim-text> <claim-text>2. Fuel cell system according to Claim 1, the sulfur sensor (36) being based on a chemical and/or electrochemical reaction, the strength of the reaction decreasing as a function of the sulfur content, in * particular the sulfur sensor (36) comprising at least one catalyst which can be poisoned by a sulfurous substance, in particular the sulfur content being determinable from the decrease of the strength of the reaction, iii particular which is measurable, for example electrically and/or thermally.</claim-text> <claim-text>3. Fuel cell system according to Claim 1 or 2, the sulfur sensor (36) being formed as a catalytic and/or electrochemical senor, in particular the sulfur sensor (36) comprising a combustion catalyst, a fuel cell dr a lambda probe.</claim-text> <claim-text>4 Fuel cell system according tc Claim 3, the catalyst of the sulfur sensor (36) comprising nickel, palladium, * platinum or mixtures thereof.</claim-text> <claim-text>5. Fuel cell system according to one of Claims 1 to 4, the sulfur sensor (36) being arranged -in the anode gas conduit (9) and/or.-in an anode waste gas conduit (25) for discharging anode waste gas from the fuel cell (2) nd/or -in a sensor conduit (37) branching off from the anode gas conduit (9) and/or from the anode waste gas conduit (25) 6. Fuel cell system according to one of Claims 1 to 5, the anode gas conduit (9) and/or the anode waste gas conduit (25) and/or the sensor conduit (37) having an inner coating, the inner coating comprising the catalyst of the sulfur sensor (36) - 7. Fuel cell system according to one qf Claims 1 to 6, the sulfur sensor (36) being arranged in gas- conducting connection, in particular in direct gas-cQnducting connection, with the desulfurisation device (10).B. Fuel cell system according to one of Claims 1 to 7, the desulfurisation device (10) having a specific flow stretch for the anode gas and the sensor conduit (37) brahching off from the desulfurisation device (10) at a place lying in a rafige from 50 to «= 90% of the :.". flow stretch for the anode gas, or the sulfur sensor (36) being arranged at a place lying in a range from »= to «= 90% of the flow stretch for the anode gas. e. * * . . * *.9. Fuel cell ystem according to one of Claims 1 to 8, -a temperature sensor (41) for determining the temperature.of the sulfur sensor (36) and/or of the sensor waste gas being provided, and the sulfur content being determinable from a decrease of the temperature of the sulfur sensor (36) and/or of the sensor waste gas, and/or -a voltage and/or current and/or resistance measuring device for determininq current, resistanceand/orvoltaqe of the sulfur sensor (36) being provided, the sulfur content being * determinable from a change of the vbltage and/or the curent and/or the resistance of the sulfur * sensor (36) 10. Fuel cell system according to one of Claims 1 to 9, the sulfur sensor (36) being in gas-conducting connection with the cathode gas conduit (15) arid/or a cathode waste gas conduit (21) for discharging cathode waste gas from the fuel cell (2), and/or an air supply.11. Fuel cell system according to one of Claims 1 to 10, the sulfur sensor (36) being beatable by a thermal coupiing to a heatabie part of the fuel cell system (1) by waste heat aising during the operation of the fuel cell system (1) - 12. Fuel cell system according to one. of Claims 1 to 11, the sulfur sensor (36) being integrated in a heat exchanger (28, 48), in a reformer (6), and/or in an * . * afterburner (23) 13. Fuel cell system according to oe of Claims 1 to 12, a * . sulfur cIiarging of the deuIfurisation device (10) being determinable as a function of the sulfur content -determined by the sulfur sehsor (36), in particular in which case a warning, in particular to renew the desulfurisation device (10), is issuable when a predetermined limit value of the sulfur charging is exceeded.24. Method for operating a fuel cell system (1),.comprisIng the methpd steps: a) leading an anode gas to the anode (3) of a fuel cell (2); * b) leading a cathode gas to the cathode (4) of a fuel cell (2); c) removing sulfurous substances from the anode gas by a desulfurisation device (10), and d) determining the concentration of sulfurous -substances in the anode gas by a sulfur sensor (36), in particular the sulfur content being determined by a sulfur poisoning of the sulfur sensor (36) 15. Use of a fuel cell system (1) according to one of Claims -1 to 10 in combined heat and power plants or engine-based coqenerators.16. A fuel ce system substantially as herein described with reference to the accompanying drawings.17. A method of operating a fuel cell system substantially as herein described with reference to the accompanying drawings. * .* * * -* .* * * * ...</claim-text>